In the stone industry it is understood that in the process of fabricating, shipping, and erection stone panel damage and/or breakage may occur. It is an accepted practice to repair damaged stone within certain limitations.

    In addition, cracks and/or breakage sometimes develop - or may be discovered - after the stone has been installed. It is the accepted practice to repair such stones under the supervision of an experienced and responsible stone expert. Such repair work should be done by qualified mechanics who have been instructed in the proper procedure, usage of specified materials, and recommended methods.

    What cannot be repaired.

    Any stone that has a crack, chips or break that compromises or in any way affects the structural integrity or the structural anchorage of the unit to the backup is NOT to be repaired but is to be replaced.

    What can be repaired.

    Damaged stone that is determined to be repairable by an expert may be repaired by one of the following methods:

    Patching: for breaks less than 3/4" in depth.

    Filling & Patching: For breaks larger than 3/4" in depth.

    Bonding: Adhesion of stone to stone.

    Patching

    This is a process where chipped or broken out areas of stone are repaired by patching the void with an epoxy mortar mix. This method is used where the broken off pieces of stone are either not available and/or the size of the chipped area is under 3/4" in depth (see SK #1).

    The subject area is to be examined to determine if the size of the break warrants, or can accommodate, "tie-in" dowel pins (see SK #1& SK #2).

    a) If the condition to be patched is of a size where steel dowel pins     cannot be properly encapsulated with the patch mix, provide an     alternative "tie-in" by drilling several 3/16" diameter "key-in" holes,     using diamond bits, at alternate approach angles (plus or minus     1-1/2" o.c. plus-or-minus 3/8" deep). This will provide a mechanical     tie-in that is in addition to the adhesion obtained by mortar mix (see SK #1).

    b) At conditions where the size of the patch can properly     encapsulate steel dowel pins, prepare the area by drilling 3/16"     diameter holes, using diamond core bits, at alternating approach     angles (see SK #2).

    Fill the holes with epoxy mortar mix and insert 1/8" diameter     stainless steel dowel pins, allowing the dowel pins to project out     into the area to be filled.

    c) If a limited break occurs on the exterior portion of a continuous     kerf, dowel pins are to be used (see SK #3).

    Note: Only exterior portions of continuous kerfs may be repaired.

    d) Place and secure edge plywood framing as, and if, required     (see SK #1 & SK #2).

    e) The area to be patched is to be clean, free of dust and dry. The     subject area should be kept free from exposure to moisture for a     minimum of 24 hours prior to the repair operation. As an added     precaution, the subject area may be further dried by the use of a     hot air blow dryer for a minimum of 5 minutes just prior to     proceeding with the patching.

    f) Prepare an "epoxy mortar mix" consisting of an approved     bonding agent, and ground stone particles, to a

    non-sag-consistency; fully fill "key-in" holes and then fill in the     balance of the chipped or broken area. Texture the surface of this     patch to resemble the adjacent finish. Once the epoxy has fully set,     rough up or hone the surface to match the flamed or honed finish     to produce a matching texture.

    When repairing polished surfaces, use a wrinkle-free polyethylene sheet to obtain a smooth shiny finish, or hand polish if necessary.

    Filling and patching

    Where the chipped or broken out area is larger than 3/4" in depth and the broken off piece of stone is not available, the area must be prepared by filling in or building up the void area with a material especially manufactured and formulated for this particular application. Then, the final surface area is to be patched and dressed using an "epoxy mortar mix" as previously described.

    a) Prepare the area to be filled by providing a mechanical tie-in by     installing 1/8" diameter bent dowel pins at alternating approach     angles in the base stone (see SK #5).

     b) Place and secure edge plywood framing as required.

     c) Clean and dry the area.

    d) Prepare a "fill mixture" of an approved bonding agent (without     any aggregate) and fill the void area completely except the top,     plus-or-minus 1/2". Allow some of the dowel pins to penetrate out     into this 1/2" area.

    e) Allow the "fill mix" to cure for a minimum of 24-hours. Then     patch the remaining area using an approved bonding agent

    Bonding.

    Bonding is used when an actual piece of the broken stone is available to be reattached and bonded back into place.

    a) The broken off piece of stone is to be placed, and temporarily     held, in proper position on the unit, and several 3/16" diameter     holes are to be drilled through the broken off piece directly into the     main base piece. The holes should be located in the "meaty"     portion of the broken off stone. The depth penetration of these     holes into the base piece is to be plus-or-minus 3/4" (see SK #6).

    b) After drilling the holes, both pieces of stone are to be cleaned     and thoroughly dried using a hot air blow dryer.

    c) Prepare an "adhesive mix" of an approved bonding agent without     any aggregate. Fill all the pre-drilled "key-in" holes with the     adhesive mix, as well as both surfaces of the stone that will come     in contact with one another. Press fit the pieces to be bonded     together and insert stainless steel dowel pins so that the pin     engagement is approximately 50% in each of the two pieces of     stone. The exposed access holes are to be patched using an     approved epoxy mortar mix with the appropriate colored granulated     aggregate to match the adjacent area. Clean off any excess     overflow and attach retaining clamps if necessary.

   d) Broken non-continuous kerf (single anchor kerf) shall NOT be     repaired. The stone should be replaced. Continuous kerf (full length     anchor kerf) broken at the outside portion can be repaired only if     the broken part can be properly re-attached with the use of     stainless steel dowel pins. Such kerf repair shall be analyzed and     substantiated with signed and sealed calculations by a licensed     professional engineer.

    Stitching.

    When a cracked or broken stone is discovered on a building - after installation - it can be repaired by "stitching" if it is determined to be repairable by an expert (see SK #7).

    To stitch a hairline crack in a vertically installed stone facing, provide a kerf cut in the exposed face of the stone, to a depth half of the stone thickness, using a diamond blade tool.

    The cut should be in the direction perpendicular to the hairline crack to receive a 1/8" diameter, 2" long stainless steel dowel.

    Install the dowel in knife-grade epoxy mixed with stone powder which will color the epoxy as close as possible to the original color of the stone.

    A minimum of one stainless steel dowel is recommended for every 6" length of hairline crack in the stone.

    If the crack is 1mm thick or more, then in addition to the stainless steel dowel stitching of the slab, provide a "V" grove 1/4" deep along the crack, and fill it with epoxy mixed with stone powder.

    Pinning.

    In addition to, or in place of,"stitching," cracked, broken or loose stone can be pinned, if determined to be repairable by an expert

    To pin a vertically installed stone facing, drill a half inch diameter hole sloping down approximately 22°, through the stone and its setting space into the concrete backup structure.

    Clean the hole with air and inject low consistency epoxy in the hole in the stone.

    Dip pre-cut stainless steel rod in epoxy and place it in the hole of the concrete and the stone approximately 1/4" short of the finished face of the stone.

    Fill the last 1/4" with epoxy and stone powder.

    Materials and tools.

    a) Patching: Use an "epoxy mortar mix" consisting of an     approved bonding agent with fine to medium grade aggregate consisting of ground particles of the actual project stone for the purpose of obtaining and matching the original project stone.

   b) Filling and Patching: "Fill mix" to be an approved bonding agent with no aggregate added.

   c) Bonding: Adhesive mix is to be made of an approved bonding agent.

   d) Stone Aggregate: Pre-packaged, dry, stone aggregate of the project stone, of a color to produce a mortar mix that matches the project stone.

   e) Factory pre-packaged proportional units of an approved bonding agent with the appropriate mixing containers.

    f) Stainless Steel Type 302 or 304 solid dowel pins or threaded rods of various lengths - straight or bent.

   g) Other Equipment: Diamond drill bits, hot air dryer, clamps, spatulas, polyethylene, tapes